A circuit break often exists in one or a plurality of columns or rows of lines of a display panel (such as TFT LCD). In order to maintain the circuit break, the TFT LCD panel is provided with maintenance lines therearound. When broken lines are found at time of final assembly of devices on the panel, the maintenance lines make the signals thereof bypass the circuit break.
FIG. 1 shows a schematic diagram of a conventional maintenance circuit for maintaining a TFT LCD panel using an operational amplifier.
FIG. 1 makes an explanation by taking a case where a broken point 2 occurs on a column line of the TFT LCD panel 1 as an example. As shown in FIG. 1, the broken point 2 is found at time of assembly of the TFT LCD panel 1, and at this moment, a panel maintenance line 5 is required to reroute a signal so as to bypass the broken point 2. Particularly, in FIG. 1, a signal outputted from a column driver 3 is connected to the panel maintenance line 5 via a panel maintenance buffer 4 formed by an operational amplifier so as to bypass the broken point 2, the output of the column driver 3 is transmitted to the other terminal of the broken column line through the panel maintenance line 5. The panel maintenance buffer 4 in FIG. 1 can be configured by the operational amplifier, the non-inverting input terminal of which is connected to an output of the column driver 3 and the inverting input terminal of which is connected to the output terminal, and this connection manner can allow the output magnification of the operational amplifier to be 1 and to be used as a voltage regulated current source. The output terminal of the operational amplifier is connected with a resistor 6 for separating the output of the column driver 3 from a capacitance on the column line to be maintained, so as to ensure stability of the buffer, and the value of the resistor 6 can be 20 to 100 ohm.
FIG. 2 is a diagram of a circuit construction showing how to maintain defective points in eight partitions X1 to X8 using four maintenance lines RP1 to RP4 each provided with a half-turn shape as known. Here, eight partitions X1 to X8 are respectively controlled by eight source driver integrated circuits (ICs) XD1 to XD8, and the maintenance line RP1 serves to maintain defective points (that is, broken points) inside the partitions X3 and X4; in other words, the maintenance line RP1 corresponds to partitions X3 and X4; the maintenance line RP2 corresponds to partitions X1 and X2; the maintenance line RP3 corresponds to partitions X5 and X6; the maintenance line RP4 corresponds to partitions X7 and X8. As known, each of the maintenance lines corresponds to two partitions, and since each of the partitions is correspondingly arranged with one source driver integrated circuit, in principle, it needs eight maintenance lines each provided with a half-turn shape to be capable of maintaining eight partitions. However, considering a limitation to space on the TFT LCD panel, only four maintenance lines each provided with a half-turn shape can be arranged around the panel.
As shown in FIG. 2, when it is detected that there exists a defective point in the partitions X1 and X2, the maintenance line RP2 is employed to reroute the signal so as to bypass the broken point, that is, to make a connection between the output from the source driver integrated circuit corresponding to the partitions X1 and X2 and the maintenance line RP2 through the operational amplifier OP1. Similarly, when it is detected that there exists a defective point in the partitions X3 and X4, the maintenance line RP1 is employed to reroute the signal so as to bypass broken point, that is, to make a connection between the output from the driver integrated circuit corresponding to the partitions X3 and X4 and the maintenance line RP1 through the operational amplifier OP2. When it is detected that there exists a defective point in the partitions X5 and X6, the maintenance line RP3 is employed to reroute the signal so as to bypass broken point, that is, to make a connection between the output from the driver integrated circuit corresponding to the partition X5 and X6 and the maintenance line RP3 through the operational amplifier OP4. When it is detected that there exists a defective point in the partitions X7 and X8, the maintenance line RP4 is employed to reroute the signal so as to bypass broken point, that is, to make a connection between the output from the driver integrated circuit corresponding to the partitions X7 and X8 and the maintenance line RP4 through the operational amplifier OP3. The specific connection manner of the operational amplifiers OP1 to OP4 in FIG. 2 is same as that of the operational amplifier as the panel maintenance buffer 4 shown in FIG. 1.
Since only four operational amplifiers OP1 to OP4 are included in the maintenance circuit as known, this kind of circuit can only detect four partitions (X1-X2, X3-X4, X5-X6, X7-X8) at the same time; that is, the operational amplifier OP1 can only maintain defective points in one partition of the partitions X1 and X2, the operational amplifier OP2 can only maintain defective points in one partition of the partitions X3 and X4, the operational amplifier OP3 can only maintain defective points in one partition of the partitions X7 and X8, and the operational amplifier OP4 can only maintain defective points in one partition of the partitions X5 and X6. If defective points exist in both of the partition X1 and X2, the defective points in partitions X1 and X2 can not be maintained at the same time.